李珥（1536-1584），號栗谷，是朝鮮時期韓國儒學的代表人物，世稱栗谷先生。他與李退溪成就了16世紀朝鮮儒學之中興。栗谷深入探討朱子學、同時批判、吸收退溪學和花潭學之後，繼而提出所謂「理通氣局」、「氣發理乘」、「七情包四端」、「矯氣質」等哲學思想。栗谷提出「理通氣局」學說，從而樹立了韓國儒學中的人物性同異論的基礎。他從「理通」的角度說明人、物性的相同，又從「氣局」的角度探討人、物性的不同。栗谷不但傳承和詮釋了朱子學，且批判地吸收在韓國儒學內進行的哲學論辯，得出具有韓國特色的學說。栗谷與其門人比較著重於探討「氣」的思想。「氣局」思想較能突顯栗谷哲學特色的思想。栗谷認為，人、物之不同不僅在於氣質的清濁或是五常之具備與否，更是其變化氣質的能力。從工夫的角度看，賢者和中人可通過修養回復本然之性，但是下等人和不肖者無法改變自己。栗谷死後，韓國儒學的人物性同異論爭，主要是從如何解釋栗谷哲學的問題上分歧的。

Yi I (1536-1584)，pen name Yulgok, is a distinguished scholar in the Korean Confucianism. With Yi T’oegye (1501-1570), he led the renaissance of Choson Neo-Confucianism in the sixteenth century. Through conducting in-depth study on Zhu Xi’s Philosophy and critically embracing T’oegye’s philosophy and Huadam’s philosophy, Yulgok developed several philosophical thoughts: li is universal and ki is particular; ki is manifest and li rides on it; seven feelings include four beginnings; transforming psychophysical form. With suggestion that li is universal and ki is particular, Yulgok established a basis for the theory that human nature and things nature are same or different in the Choson Neo-Confucianism. From the perspective that li is universal, he claimed that human nature and things nature are same. From the perspective that ki is particular, he argued that human nature and things nature are different. According to Yulgok, human being and things are different not only in the purity of psychophysical form or in the presence of five virtues but also in the ability to change psychophysical form. From the perspective of self-cultivation, both sage and mediocrities are able to restore original nature through practice but the inferior are unable to do so. After Yulgok passed away, the debate that human nature and things nature are same or different in the Choson Neo-Confucianism began to diverge on the question of how to interpret Yulgok’s Philosophy.